Retroreflective transfer sheet material

ABSTRACT

A transfer sheet material for forming retroreflective graphic images on a substrate, the sheet material comprising a monolayer of transparent microspheres; a color layer printed over the microspheres in a first graphic segment of the sheet material in an imagewise pattern, the color layer comprising a colorant in a transparent resin; a reflective layer printed over the microspheres in a second graphic segment of the sheet material in an imagewise pattern, the reflective layer comprising reflective flakes in a transparent binder, wherein the microspheres are partially embedded in at least one of the color layer and the reflective layer, individual microspheres having the reflective flakes arranged in cup-like fashion about their embedded portions; and a bonding layer printed over the color layer and the reflective layer, the bonding layer being sufficiently thick to embed all exposed surfaces of the color layer and the reflective layer and being adapted for use in securing the sheet material to a substrate. Also, a method for making such a sheet material. Also, a sheet material having the color layer and the reflective layer combined as a single layer. Also, a sheet material having a graphic segment in which a specularly reflective metal layer is deposited over the microspheres.

This is a continuation-in-part of application Ser. No. 08/058,155, filedMay 5, 1993, now U.S. Pat. No. 5,344,705.

FIELD OF INVENTION

The present invention relates to retroreflective transfer sheetmaterials which are useful for forming retroreflective graphic images onsubstrates and to a process for making such sheet materials.

BACKGROUND

During the growth in popularity of decorative emblems on garments suchas T-shirts or jackets, there has been a continuing desire for ways tomake such emblems retroreflective. On an outer garment worn at night,such retroreflective emblems would provide a bright return of light tooncoming motorists, thereby adding a safety feature, as well asincreased decorative appeal, to the garments.

Insofar as known, no one has previously found a practical orcommercially useful way to provide such retroreflective emblems. Somehave proposed silk-screening a design onto a garment, and then while thedesign is still wet, cascading microspheres onto the design; but such anapproach is messy, usually provides a nonuniform deposit ofmicrospheres, and is impractical for obtaining high reflectivebrightness (which requires that the embedded surfaces of themicrospheres be covered with a specularly reflective layer). Others haveproposed mixing hemispherically specularly-coated glass microspheresinto ink and printing such an ink onto the garment (see U.S. Pat. No.3,535,019 (Longlet et al.)); but while such a product is useful for somepurposes, it provides a reduced retroreflective brightness because thehemispherically-coated microspheres are randomly oriented within anapplied coating. Still others long ago proposed the preparation ofretroreflective decals comprising a layer of glass microspheres disposedover a printed design (see U.S. Pat. No. 2,422,256 (Phillippi)); but thesuggested decal was a several-layer product which was likely stiff andunsuited for conformable garments.

In the past, the only commercial products suitable for retroreflectiveemblems or markings on garments have generally been single-colored tapesor sheet materials, with constructions as described in U.S. Pat. No.2,567,233 (Palmquist et al.); U.S. Pat. No. 3,551,025 (Bingham et al.);U.S. Pat. No. 3,700,305 (Bingham); and U.S. Pat. No. 3,758,192(Bingham). But none of these commercial products is useful to form thecomplex multi-colored designs that are in fashion and are needed tomaximize the use of retroreflective emblems.

U.S. Pat. No. 4,102,562 (Harper et al.) and published InternationalApplication No. PCT/DK91/00325 (Publication No. WO 92/07990) discloseretroreflective transfer sheet materials comprising a carrier, acontinuous monolayer of transparent microspheres partially embedded inthe carrier, a specularly reflective layer (typically a transparentdielectric mirror) deposited onto the exposed surfaces of themicrospheres, and a color layer printed over the microsphere layer in animagewise pattern. In each reference, if the specularly reflective layeris a transparent dielectric mirror, the imagewise pattern or graphicdesign of the color layer is visible underneath the layer ofmicrospheres in daylight. Although the daytime appearance of theresulting transferred emblem is similar to that obtained with heattransfers that carry no layer of microspheres (i.e., non-reflectivetransfers), when the emblem is illuminated in a dark room, the lightretroreflected from the emblem optically masks the graphic design of theunderlying color layer. In other words, only the color of the incidentlight is typically retroreflected from the emblem since the light isretroreflected directly from the dielectric mirror substantially withoutcontacting the underlying graphic design.

The result is that, in spite of the above-described efforts,multi-colored designs or emblems on garments continue to be madenon-retroreflective and the potential use of such emblems for safetypurposes goes unrealized.

U.S. Pat. No. 5,229,882 (Rowland) and United Kingdom patent applicationGB 2 245 219A disclose retroreflective sheet materials which are adaptedto be used as retroreflective tapes and patches for clothing and asretroreflective vests and belts. The sheet material can be made byproviding a sheet material body member with microprisms, applying areflective metallic deposit on the microprisms, applying a coating of aprotective material in a grid pattern over the metallic deposit,exposing the coated surface to a solvent which removes the metallicdeposit in the unprotected areas, and then using a colored adhesive tobond the resulting laminate to a substrate.

SUMMARY OF INVENTION

The present invention provides a novel transfer sheet material which isuseful for forming retroreflective graphic images on a substrate,including fabrics as well as other substrates. This new transfer sheetmaterial comprises:

a) a monolayer of transparent microspheres, typically preferably closelypacked;

b) a color layer printed over the microspheres in a first graphicsegment of the sheet material in an imagewise pattern, the color layercomprising a colorant in a transparent resin;

c) a reflective layer printed over the microspheres in a second graphicsegment of the sheet material in an imagewise pattern in such a mannerthat any overlapping areas of the first and second graphic segments arecharacterized by the color layer being disposed between the microspheresand the reflective layer, the reflective layer comprising reflectiveflakes in a transparent binder, wherein the microspheres are partiallyembedded in at least one of the color layer and the reflective layer,the reflective flakes being small enough relative to the microspheresthat individual microspheres have the reflective flakes arranged incup-like fashion about their embedded portions; and

d) a bonding layer printed over the color layer and the reflectivelayer, the bonding layer being sufficiently thick to embed all exposedsurfaces of the color layer and the reflective layer and being adaptedfor use in securing the sheet material to a substrate.

In another of its aspects, the invention relates to a method for makingthe above-described transfer sheet material, comprising:

a) providing a carrier comprising a base sheet and a heat-softenablelayer on the base sheet;

b) cascading a monolayer of transparent microspheres onto theheat-softenable layer and embedding the microspheres in theheat-softenable layer to a depth averaging between about 25 and about 50percent of their diameters;

c) printing onto the microspheres in a first graphic segment of thesheet material in an imagewise pattern with a colorant compositioncomprising a colorant in a transparent resin and drying the colorantcomposition to form a color layer;

d) thereafter printing onto the microspheres in a second graphic segmentof the sheet material in an imagewise pattern with a reflective layercomposition in such a manner that any overlapping areas of the first andsecond graphic segments are characterized by the color layer beingdisposed between the microspheres and the reflective layer composition,the reflective layer composition comprising reflective flakes in atransparent binder, and drying the reflective layer composition to forma reflective layer, wherein the microspheres are partially embedded inat least one of the color layer and the reflective layer, the reflectiveflakes being small enough relative to the microspheres that individualmicrospheres have the reflective flakes arranged in cup-like fashionabout their embedded portions; and

e) thereafter printing onto the first and second graphic segments of thesheet material with a bonding composition to a depth sufficient to embedall exposed surfaces of the color layer and the reflective layer anddrying the bonding composition to form a bonding layer and the completedsheet material, the bonding layer being adapted for use in subsequentlyadhesively bonding the sheet material to a substrate.

In another of its aspects, the invention relates to transfer sheetmaterials comprising a layer of specularly reflective metal interposedbetween the transparent microspheres and the adjacent bonding layer inany graphic segment designated to have a gray or silver color and astrong retroreflective brightness. Typically, the specularly reflectivemetal layer is disposed in an imagewise pattern.

In yet another of its aspects, the invention relates to transfer sheetmaterials comprising a colored reflective layer instead of a separatecolor layer and a separate reflective layer. The colored reflectivelayer comprises both a colorant and reflective flakes in a transparentresin and is printed over the transparent microspheres in a singleprinting step.

Sheet materials of the invention can be used to provide substrates withgraphic images comprising non-reflecting colored areas andretroreflective areas, with at least some of the retroreflective areastypically being capable of brilliantly retroreflecting the color of theimage provided in these areas. Fabric substrates comprising suchtransferred graphic images can exhibit good wash durability (i.e.,launderability) and can also exhibit good drycleaning durability.

BRIEF DESCRIPTION OF DRAWING

The invention will be further explained with reference to the drawing,wherein:

FIG. 1 is an enlarged sectional view through a portion of aretroreflective transfer sheet material of the invention;

FIG. 2 illustrates schematically in a sectional view the application ofa portion of a transfer sheet material of the invention to a substrate;

FIG. 3 is a top plan view of an illustrative emblem transferred onto asubstrate according to the invention;

FIG. 4 is an enlarged sectional view through a portion of anotherembodiment of a transfer sheet material of the invention; and

FIG. 5 is an enlarged sectional view through a portion of yet anotherembodiment of a transfer sheet material of the invention.

These figures, which are idealized, are not to scale and are intended tobe merely illustrative and nonlimiting.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A retroreflective transfer sheet material 10 as shown in FIG. 1 can beprepared by cascading a monolayer of transparent microspheres 12 onto acarrier 14 which typically comprises a base sheet 16 and aheat-softenable layer 18. For example, the base sheet 16 can comprise aKraft paper or a heat-resistant polyester foil, and the heat-softenablelayer 18 can comprise a wax, silicone, or rapidly-setting polyolefinsuch as a low-density polyethylene. The microspheres 12 are typicallythermally sunk into the heat-softenable layer 18 to a depth of betweenabout 25 and about 50 percent of their diameters, and preferably betweenabout 40 and about 50 percent of their diameters, by passing the carrier14 and monolayer of microspheres through a tunnel oven set at atemperature in the range of about 225° to about 300° F. (107° to 149°C.).

The transparent microspheres 12 typically are made of glass andtypically have diameters between about 25 and about 150 microns,preferably between about 60 and about 100 microns. Best results aregenerally obtained when the microspheres have uniform sizes. For bestreflective properties, their index of refraction should be about 1.9.The microspheres are preferably as clear as possible.

The sheet material 10 comprises a first graphic segment 20 which can bediscontinuous as shown in FIG. 1. In the first graphic segment 20, theexposed surfaces of the microspheres are "printed" with a colorantcomposition to form a color layer 22. The term "printed" is usedthroughout this description in a generic sense and is intended toinclude any specific imagewise coating, spraying, printing,lithographing, screen printing, hand painting, or other suitableapplication process. In other words, the term "first graphic segment" isintended to denote a segment of the sheet material 10 which is providedwith the color layer 22. The color layer 22 is typically formed byscreen printing the colorant composition in an imagewise pattern ontothe microspheres using a printing screen typically having a woven meshcount per centimeter (Mc/cm) of about 44 to about 90.

It is preferred that a screen having a woven mesh count per centimeterof about 77 be used in printing the color layer 22 over the microspheresbecause portions of the resulting sheet material which are both coloredand retroreflective provide a distinct retroreflection of the appliedcolor when this screen size is used. A coarser mesh screen can be usedbut will result in a thicker color layer, less retroreflection, and adeeper color; whereas a finer mesh screen will result in a thinner colorlayer, more retroreflection, and a brighter color.

The color layer 22 is usually printed in a reverse image so that apositive image is formed when the sheet material 10 is transferred to asubstrate. After the colorant composition is printed onto themicrospheres, the colorant composition is dried, typically in aninfrared oven at about 120° C. for about 30 seconds, to evaporate thesolvent present in the colorant composition.

If desired, the color layer 22 can be formed by successively printing(typically screen printing in an imagewise pattern) and drying aplurality of colorant compositions onto the microspheres in the firstgraphic segment 20. In other words, the color layer 22 can comprise anumber of different colors for each color of a multi-colored design orcan comprise a number of differently colored layers to produce anadditive or "hybrid" color, each layer being formed by a separatelyprinted and dried colorant composition. For example, if two differentlycolored colorant compositions are printed in layers which do notoverlap, these layers will contribute to a multi-colored design. On theother hand, two differently colored colorant compositions can be printedin layers which do overlap to achieve an additive color. For example, ifa sheet material of the invention includes overlapping layers of yellowand blue, these layers will provide a green hue or hybrid color to thesheet material in the area of these layers.

The colorant composition of the color layer 22 typically comprises a"two-component" transparent resin which includes a colorant in the formof a transparent pigment or dye substantially uniformly dispersed in thetransparent resin in a concentration sufficient to produce the desiredintensity of color. The "first component" is typically in the form of aprintable paste which is typically preferably as clear and transparentas possible and can, for example, comprise the following materials:

    ______________________________________    Component             Parts by Weight    ______________________________________    Polyvinyl Chloride Acetate                          6    Polyurethane Resin    15    Transparent Pigment   9    Ketone Solvent (e.g., Cyclohexanone)                          70    ______________________________________

The first component is admixed with about 1 to about 5 parts by volumeof a suitable hardener, typically an isocyanate hardener such as NB 386,a hexamethylene diisocyanate available from Sericol Group Limited,Westwood Road, Broadstairs, Kent CT10 2PA, England, which serves as thesecond component. It is also typically important that the secondcomponent be as clear and transparent as possible.

It has been discovered that polyurethane-based colorant compositionswork well because they adhere well to the rear surfaces of themicrospheres and exhibit good stretchability and flexibility, and thusfavorably contribute to the durability of sheet materials of theinvention. Suitable colorant compositions can also be made by using apolyester resin as the transparent resin in the colorant composition.

It is typically desirable to utilize materials in the colorantcomposition which will not crystallize upon being exposed totemperatures up to about 210° C. since heat is typically used in theabove-described drying step and in transferring the sheet material to asubstrate (described below).

The viscosity of the colorant composition is important because it istypically desired to have the colorant composition conform to themicrospheres. Also, the colorant composition should not flow undesirablyso as to result in limited graphic image resolution. The viscosity ofthe colorant composition can be adjusted as desired by adding a thinnersuch as a butoxy ethanol to the colorant composition until the desiredviscosity is achieved.

After application of the color layer 22, a second graphic segment 24 ofthe sheet material 10 is provided with a reflective layer 26 disposedbehind and printed over the microspheres 12. In other words, the term"second graphic segment" is intended to denote a segment of the sheetmaterial 10 provided with the reflective layer 26. Like the color layer,the reflective layer is typically screen printed in an imagewise patternby Use of a printing screen typically having a woven mesh count percentimeter of about 44 to about 90, and the reflective layer issubsequently dried in a similar fashion.

As shown in FIG. 1, both the color layer 22 and the reflective layer 26can be continuous or discontinuous and can overlap in certain locationsor segments and not overlap in other locations. In other words, thefirst graphic segment 20 and the second graphic segment 24 can becontinuous or discontinuous and can overlap in certain locations and notoverlap in other locations. In locations where the color layer and thereflective layer overlap, the color layer is disposed between themicrospheres and the reflective layer to provide a segment of the sheetmaterial which is capable of retroreflecting the color of the colorlayer when the microspheres in this segment are illuminated with a beamof incident light.

The reflective layer 26 typically comprises a reflective layercomposition comprising a transparent binder which is compatible (i.e.,will adhere thereto without causing or undergoing undesirabledegradation) with the transparent resin used in the colorant compositionand further comprises 15 parts by weight of a powder comprisingreflective flakes. An illustrative reflective layer composition is asfollows:

    ______________________________________    Component             Parts by Weight    ______________________________________    Polyester Binder Resin Composition                          15    Reflective Flake Powder                          15    Ketone Solvent (e.g., Cyclohexanone)                          70    ______________________________________

The polyester binder resin composition can comprise a Nylobag™ orNylotex™ polyester extender resin available from Sericol Group Limited.Incidentally, it is believed that a polyurethane binder resin could besubstituted for the polyester binder resin although polyester binderresin is typically used. The reflective flakes will typically be metalflakes, e.g., aluminum, bronze, or gold flakes, although other suitableflakes such as nacreous pigment particles (sometimes called pearlescentpigments) as disclosed in U.S. Pat. No. 3,758,192 (Bingham) may be usedif desired. Further, it is also contemplated that plastic andmetal-plated plastic reflective flakes could be employed.

The above component mixture is admixed with about 1 to about 5 parts byvolume of a suitable hardener, typically NB 386 hexamethylenediisocyanate hardener from Sericol Group Limited. Like the colorantcomposition, it is important that the binder be as clear and transparentas possible.

The reflective flakes are typically much smaller than the microspheresand preferably are microscopic in that they are believed to have athickness in the range of about 0.03 to about 0.8 microns although themeasurement of the thickness of reflective flakes is a very inexactscience at the present time. Because the reflective flakes are so muchsmaller than the microspheres, they can generally conform to thesurfaces of the microspheres or the contoured surfaces of the colorlayer. In other words, after printing of the reflective layer, themicrospheres are partially embedded in either the color layer or thereflective layer, with certain of the microspheres typically havingreflective flakes arranged in cup-like fashion about their embeddedportions. A suitable aluminum flake powder can be obtained under thetrade designation Miral™ 80,000/A/cx/70-30 from A. van Lerberghe,Elleboogstraat 7, 8500 Kortrijk, Belgium.

As shown at the left side of FIG. 1, certain segments of the sheetmaterial 10 are located within the first graphic segment 20 but notwithin the second graphic segment 24. The microspheres 12 in thesesegments are printed with the color layer 22 but not the reflectivelayer 26. These segments of the sheet material have colored graphics butthe graphics are not intended to be retroreflective. The color layer 22and reflective layer 26 are typically printed in layers so thin thatneither contains sufficient substance to be capable of bonding themicrospheres together and to a substrate. Thus, a relatively thickbonding layer 28 is provided and is adapted for use in bonding the sheetmaterial 10 to a substrate 30 (substrate 30 is shown in FIG. 2). Whenthe sheet material 10 is intended to be used in transferring a design toa fabric substrate, there should typically be enough material in thebonding layer to penetrate the fabric and thereby attach the transferreddesign to the fabric. The bonding layer 28 also functions to bond themicrospheres 12 together. The bonding layer 28 is formed by printing abonding composition in an imagewise fashion, typically by a screenprinting process, over the color layer 22 and the reflective layer 26.Thus, the bonding composition is applied only within the first andsecond graphic segments, and is not applied in areas of the sheetmaterial located outside of the first and second graphic areas. Thebonding composition is printed in an amount which is at least sufficientto embed all exposed surfaces of the color layer 22 and the reflectivelayer 26 and is subsequently dried in the same fashion as the colorantcomposition. Typically, the bonding layer 28 has a wet thickness ofabout 50 to about 100 microns. Such a wet thickness can be achieved byusing a fabric printing screen having a woven mesh count per centimeter(Mc/cm) of about 44 to about 90.

The bonding composition preferably comprises an extender resin and aheat-activatable, hot-melt transfer adhesive powder fused into theextender resin, i.e., the adhesive powder is embedded in and bonded tothe extender resin. With this preferred type of bonding composition, theextender resin is typically printed in imagewise fashion but theadhesive powder is fused into the extender resin by any suitableprocess, not necessarily by printing in an imagewise fashion.

The extender resin typically comprises the following components:

    ______________________________________    Component             Parts by Weight    ______________________________________    Polyester Resin       25    Ketone Solvent (e.g., Cyclohexanone)                          75    ______________________________________

The polyester resin can comprise a Nylobag™ or Nylotex™ polyesterextender resin available from Sericol Group Limited. Also, it isbelieved that polyurethane resin could be substituted for the polyesterresin although polyester resin is typically used. The above componentmixture is admixed with about 1 to about 5 parts by volume of a suitablehardener, typically an isocyanate hardener such as NB 386 hexamethylenediisocyanate hardener from Sericol Group Limited.

While the applied extender resin is still wet, the elastomeric powder isapplied over the surface of the extender resin by any suitable techniqueknown in the art and then fused into the extender resin. This fusing istypically achieved by heating the extender resin and adhesive powder inan infrared oven at about 130° to about 250° C. for about 10 to about 40seconds, more preferably at about 150° to about 250° C. for about 20 toabout 30 seconds, and most preferably at about 200° C. for about 25seconds. The powder fuses into the extender resin such that at leastsome of the powder particles are firmly embedded in the extender resinbut also partially exposed at the extender resin surface locatedopposite the microspheres. These particles promote bonding of the sheetmaterial 10 to the substrate 30.

The transfer adhesive powder is a fine granulate which is typicallybased on polyester or polyamide. Examples of suitable adhesive powdersinclude a polyamide resin powder which is available under the tradedesignation FT-409 Transfer Powder from Sericol Group Limited; and apolyester (polydiol dicarboxylate) resin powder which is available underthe trade designation Avabond 48E Powder from Imperial Chemical House ofLondon, England.

The adhesive powder promotes the laundering and drycleaning durabilityof the transferred image or emblem and increases the likelihood that thebonding layer 28 will be heat-activatable for purposes ofheat-transferring the emblem 32 from the sheet material 10 to thesubstrate 30 even after long-term storage of the sheet material. It hasalso been found that the adhesive powder promotes adhesion between thesheet material 10 and textile substrates, thereby allowing the carrier14 to be stripped off (separated from the color layer 22 and thereflective layer 26) after transferring the image or emblem of the sheetmaterial 10 to a substrate.

Alternatively, it has been found that the extender resin of the bondingcomposition can be replaced with a transfer glue which is typically apolyester-based glue such as the transfer glue sold by Unitika SparkliteCo. of Japan under the trade designation TR Glue. This transfer gluecomprises:

a) 25 parts by weight of a crystalline saturated polyethyleneterephthalate resin in powder form having a melting point of 110° C. andavailable from Toyobo of Japan under the trade designation Vylon™GN-915P; and

b) 75 parts by weight of a saturated polyethylene terephthalate resin inliquid form (50 weight percent saturated polyester resin and 50 weightpercent cyclohexanone solvent), the liquid resin having a viscosity of5,000 centipoise at about 20° C. and being available from Toyobo underthe trade designation Vylon™ RV-51CS.

The transfer glue is prepared by adding the crystalline polyester to theliquid polyester while stirring the liquid polyester. The transfer gluehas a viscosity of about 90,000 centipoise at about 20° C. and a resincontent of about 62.5 weight percent.

Such transfer glues based on polyester do not need a hardener for theirfunction, but they take a somewhat longer time to dry than theabove-discussed two-component colorant compositions, reflective layercompositions, and extender resin bonding compositions. For example, thetransfer glue is typically dried in an oven at about 50° to about 60° C.for a time of from about 3 to about 5 hours, or at room temperature forseveral days. Further, these transfer glues can be used without fusingan adhesive powder into them if no special demands for durability are tobe met. However, if the sheet material 10 is to be transferred ontosubstrates which are typically laundered at temperatures above about 50°C., it will typically be desirable to fuse one of the above adhesivepowders into the transfer glue in the same manner described above inconnection with the extender resin.

Referring to FIG. 2, an emblem or design 32 of the completed sheetmaterial 10 can be transferred to the substrate 30 as shown. Thisdrawing figure is a schematic view, as it is contemplated that thebonding layer 28 can bond to the substrate 30 by penetrating throughopenings in the top surface of the substrate 30, such penetration notbeing shown in this figure. As seen, all of the emblem 32 is design. Theemblem 32 generally comprises the microspheres 12, the color layer 22,the reflective layer 26, and the bonding layer 28. The substrate 30 ontowhich the emblem 32 is transferred will typically be flexible andcomprise a natural or synthetic fabric, such as a cotton,cotton-polyester blend, or nylon, a film, or a nonwoven material.

The transfer is typically accomplished by laying the completed sheetmaterial 10 against the substrate 30 with the bonding layer 28 facingthe substrate 30 and placing this assembly in a heat-transfer machineset between about 130° and about 210° C., where pressure is typicallyapplied for between about 10 and about 30 seconds. During this time, thebonding layer 28 softens and typically penetrates into the substrate 30through openings in the surface of the substrate. The assembly is thenpermitted to cool so that the bonding layer 28 exhibits a strongadhesion to bond the transferred emblem to the substrate. The carrier 14can then be peeled back and removed to thereby transfer the emblem 32onto the substrate 30 as shown in FIG. 2. The microspheres 12 separatefrom the carrier 14 and are partially exposed with their uncoveredsurfaces facing outwardly and their embedded surfaces embedded in thecolor layer 22 or the reflective layer 26.

The result is that retroreflective emblems having the same order ofdefinition of design obtained in non-retroreflective heat-transferredemblems may be obtained. Multi-colored, intricately patterned designsmay be formed, and the designs may be formed with graphic segments whichare colored, retroreflective, or both colored and retroreflective. Thegraphic segments which are both colored and retroreflective can beilluminated with a light beam which brilliantly retroreflects in thecolor of the underlying graphic design. This brilliant, coloredretroreflection occurs because the incident light rays pass through thecolor layer both before and after being reflected by the reflectivelayer. The color layer filters the light rays as they pass through thecolorant of the color layer, and the filter action produces a color huein these light rays. Increasing the proportion of colorant in the colorlayer tends to deepen the color produced, whereas decreasing theproportion of colorant in the color layer weakens the color produced,thereby providing a lighter color hue.

The transfer sheet material 10 is typically very thin so that garmentsubstrates reflectorized with them are of substantially the sameconformability or drapability as garments with non-reflective emblems.Also, transfer of emblems from the sheet materials onto garmentsubstrates can be achieved using the same general, procedures andequipment already used in the fabric industry.

It is contemplated that the bonding layer 28 could comprise othermaterials provided the materials retain an imagewise pattern throughouta transfer operation. For example, one such material, apressure-sensitive adhesive, would have adhesive properties withoutbeing heated. If the bonding layer 28 were to comprise such an adhesive,the sheet material 10 would typically include a release liner coveringthe adhesive surface of the bonding layer.

A representative transferred design or emblem 132 is illustrated in FIG.3. This particular emblem 132 is in the form a bull's eye comprising ablue hub 134 in its center, a green doughnut-shaped graphic segment 136disposed radially outwardly (i.e., concentrically) from the blue hub,and a blue doughnut-shaped graphic segment 138 disposed radiallyoutwardly from the green doughnut-shaped segment.

If a light is illuminated on a segment of the sheet material wherein thefirst and second graphic segments overlap, light will retroreflect fromthis segment in such a manner that the underlying colored graphics arealso visible and have a brilliant, colored retroreflective appearance inareas of the sheet material 10 where only one of the first or secondgraphic segments is provided (i.e., there is no overlapping), either thecolor layer 22 or the reflective layer 26 will be disposed behind themicrospheres 12. If only the color layer 22 is disposed behind themicrospheres 12, the graphic design of the color layer in this segmentof the sheet material 10 will be visible but will not beretroreflective. If only the reflective layer 26 is disposed behind themicrospheres 12, the reflective layer in this segment of the sheetmaterial 10 will have a silvery daytime appearance, and willretroreflect any incident beams of light, but will not be capable ofretroreflecting light in a color different from the color of theincident light. If it were desired to produce an emblem comprising onlyuncolored retroreflecting areas, the sheet material 10 could be providedwith no color layer 22 but still be provided with the reflective layer26.

It is also contemplated that sheet materials of the invention cancomprise a specularly reflective metal layer which is applied, typicallyby a vapor-coating process, over the microspheres to form a specularlyreflective layer. This concept as well as the use of a plurality ofdifferently colored colorant layers which overlap each other areillustrated in FIG. 4. As shown therein, a retroreflective transfersheet material 40 comprises a carrier 41 which in turn typicallycomprises a base sheet 42 coated with a heat-softenable layer 43. Amonolayer of transparent microspheres 44 is shown embedded into thesurface of the heat-softenable layer 43, as discussed above inconnection with FIG. 1. In a first graphic segment 45 of the transfersheet material, a thin (e.g., a thickness of about 500 to about 1200Angstroms) metal layer 46 typically comprising vapor-coated aluminum isbonded to those surfaces of the microspheres 44 which are not in contactwith the heat-softenable layer 43. In another graphic segment 48 of thesheet material, a first color layer 47 contacts the surfaces of themicrospheres which are not embedded in the heat-softenable layer 43. Ina graphic segment 50, a second color layer 49 overlies the microspheres.Also, in an additive color segment 51 of the transfer sheet material,the second color layer 49 overlies the first color layer 47. Further, areflective layer 52, typically comprising reflective flakes in atransparent binder as described in previous embodiments, is printed overall areas of the colored graphic segments 48, 50. Lastly, a bondinglayer 53 is printed over the thin metal layer 46 and the reflectivelayer 52 in all areas of the graphic segments 45, 48, 50.

As in the sheet material of FIG. 2, an outer surface 54 of the bondinglayer 53 is adapted to be bonded to a fabric (not shown), and thecarrier 41 is adapted to be stripped off to expose the surfaces of thetransparent microspheres. In use, the resulting retroreflective graphicimage transfer will have exceptional retroreflective brightness and agenerally gray color in the graphic segment 45, a first coloredretroreflective appearance in areas of the graphic segment 48 notcoinciding with the graphic segment 51, a second colored retroreflectiveappearance in the graphic segment 50, and a third coloredretroreflective appearance in the graphic segment 51 resulting from thecombined or additive effect of the first color layer 47 and the secondcolor layer 49.

The transfer sheet material 40 can be made by providing a carrier 41comprising a polyethylene terephthalate base sheet 42 and a polyethylenelayer 43 on one side of the base sheet 42. A densely-packed monolayer oftransparent glass microspheres (60-100 micron diameter) 44 can bepartially embedded in the polyethylene layer 43 by cascading themicrospheres 44 onto the polyethylene layer 43 and heating thepolyethylene to a temperature in the range of about 107°-148° C.(225°-300° F.) to allow the microspheres 44 to settle into thepolyethylene surface to a depth of about 15-50 microns. An 800 Angstromsthick aluminum layer 46 can then be vapor-coated onto the exposedsurfaces of the glass microspheres 44 over substantially the entiresheet material.

The resulting sheet material can then be positioned on the workingsurface of a screen printing table so that the aluminum-coated surfaceof the glass microspheres faces upward. The screen printing table can befitted with a screen which carries the image of one or more graphicsegments 45 which are designated to be gray and stronglyretroreflective. A layer of the same two-component extender resin (e.g.,Nylobag™ or Nylotex™ polyester resin, solvent and hardener) used for thebonding layer of FIG. 1 can then be screen printed in an imagewisepattern over the aluminum layer 46 in the graphic segments 45 andallowed to dry. However, the isocyanate hardener need not necessarily beused, particularly if more elasticity is desired and wash durability canbe sacrificed to some extent. The sheet material is then contacted with(preferably immersed in) a dilute aqueous etchant solution until theunprotected metal areas of the metal layer 46 have been visibly etchedaway. The aqueous etchant solution can be formulated by dissolving asuitable powder into water. One powder found to be useful is a draincleaning powder sold under the trade designation Plumbo™ byKreftinginvest A/S of Oslo, Norway. This powder is believed to have asolids content of approximately 30-50 weight percent sodium hydroxide,30-60 weight percent sodium bicarbonate, and 5-10 weight percentaluminum. The sheet material is then removed, washed with water, anddried.

The above powder can be conveniently used because it is a commerciallyavailable product, but it is believed that other aqueous solutions (suchas a 25% by weight solution) of sodium hydroxide in water would beequally effective and possibly preferred. In the graphic segments 45,the extender base resin provides a protective coating for the aluminumcoating underlying the extender base so that the etching process doesnot remove the vapor-coated aluminum in these areas of the transfersheet material. In areas of the transfer sheet material which are notprotected by the extender base, the aluminum coating is etched awaybecause the etchant solution is capable of dissolving the vapor-coatedaluminum. The first color layer 47, second color layer 49, andreflective layer 52 comprising aluminum flakes in a transparent binderare then printed in their respective graphic segments of the sheetmaterial. The bonding layer 53 is then printed in the graphic segments45, 48, 50.

It is further contemplated that in areas where a color layer and areflective layer might otherwise overlap, these distinct layers may bereplaced by a colored reflective layer comprising a colorant andreflective flakes in a transparent resin, the colored reflective layertypically being applied in a single printing step. As shown in FIG. 5, aretroreflective transfer sheet material 60 comprises a carrier 61 whichtypically comprises a base sheet 62 coated with a heat-softenable layer63. A monolayer of transparent microspheres 64 is embedded into thesurface of the heat-softenable layer 63, as discussed above inconnection with FIGS. 1 and 4. A first colored reflective layer 65,comprising a first colorant and reflective flakes in a transparentresin, is typically applied in an imagewise pattern over the transparentmicrospheres 64 in a first graphic segment 66 of the sheet material. Asecond colored reflective layer 67, comprising a second colorant andreflective flakes in a transparent resin, is typically applied in animagewise pattern over the transparent microspheres 64 in a secondgraphic segment 68 of the sheet material. A reflective layer 69,comprising only reflective flakes in a transparent resin, can also beapplied, typically in an imagewise pattern, over the transparentmicrospheres 64 in a third graphic segment 70. A bonding layer 71 canthen be printed over the layers 65, 67, 69 in the graphic segments 66,68, 70. In use, the resulting retroreflective graphic image transferwill provide a first colored retroreflective appearance in the graphicsegment 66, a second colored retroreflective appearance in the graphicsegment 68, and a gray colored, strongly retroreflective appearance inthe graphic segment 70.

This concept of combining a colorant and reflective flakes in a singlecolored reflective layer can also be used in connection with the aboveembodiment in which a thin layer of specularly reflective metal isdeposited directly onto the transparent microspheres. For instance,although not illustrated in FIG. 4, the second color layer 49 and thereflective layer 52 could be replaced by a single colored reflectivelayer comprising a colorant and reflective flakes in a transparentresin.

The transfer sheet material 60 illustrated in FIG. 5 can be made byfitting a screen printing table with a screen which carries the image ofa first graphic segment 66 designated to be of a first color andretroreflective. Then, a first colored reflective layer 65 comprisingtransparent resin, a first colorant material such as a transparent dyeor pigment, and aluminum reflective flakes is printed onto the exposedsurfaces of transparent glass microspheres 64 in the graphic segment 66.During this printing step, the microspheres 64 are embedded in a carrier61 comprising a paper base sheet 62 and a 50 micron thick layer ofpolyethylene 63 on one side of the base sheet. The screen printing tablebeing utilized can then be fitted with a different screen which carriesthe image of a second graphic segment 68 designated to be of a secondcolor and retroreflective. The second colored reflective layer 67 canthen be printed and allowed to dry. The screen printing table can thenbe fitted with a third screen which carries the image of a third graphicsegment 70 designated to be gray and strongly retroreflective. Areflective layer 69 comprising transparent resin and aluminum reflectiveflakes is then screen printed in the third graphic segment 70 andallowed to dry. Finally, the screen printing table can be fitted with ascreen which carries the image of a fourth graphic segment 72 comprisingall areas of the first, second, and third graphic segments 66, 68, 70respectively. A bonding layer 71 is then formed in the fourth graphicsegment 72 by printing a two-component extender resin composition in thefourth graphic segment 72 and then fusing a transfer adhesive powderinto the extender resin as described above in connection with the firstembodiment.

EXAMPLES

The invention will be further explained by the following illustrativeexamples which are intended to be nonlimiting. Unless otherwiseindicated, all amounts are expressed in parts by weight.

A conveniently sized sheet of a retroreflective transfer sheet materialof the invention is positioned on the working surface of a screenprinting table so that the transparent microspheres are facing upward. Atable which is equipped with a vacuum device for holding the sheet in adesired position is preferred. The screen printing table is fitted witha screen which carries the desired art image: any emulsion used toprepare direct printing screens, such as Advance Direct Photo EmulsionDM 747, is suitable for preparing transfer image screens. When preparedwith a 150-200 mesh per inch (60-80 mesh per centimeter) T threadscreen, the image should be expected to display the desired range ofretroreflective colors. Using standard practices well known to thoseskilled in the screen printing art, the first of the desired colors ofthe transfer image is printed through the screen usingpolyurethane-based inks containing transparent pigments. A typical inkcomposition would contain:

    ______________________________________    6%           Polyvinylchloride Acetate    15%          Polyurethane Resin    9%           Transparent Pigment    1-5%         Isocyanate Hardener                 Solvent as required    ______________________________________

While the first color prints are being prepared, they may be held atambient conditions until they are all printed, then dried according tothe ink manufacturer's directions, if necessary. When the prints withthe first color are all dried they may be printed and dried withsubsequent colors until all the desired colored portions of the imageare complete.

The reflective layer can be printed through a printing screen whichbears the transfer image of the portion of the final image which isdesired to be retroreflective. A 75-200 mesh screen made with T threadmay be used for application of the reflective layer. The reflectivelayer can be prepared by mixing up to 30% of the reflective flake (suchas Miral™ 80000/A/cx/70-30, available from A. van Lerberghe,Elleboogstraat 7, 8500 Kortrijk, Belgium) into a clear extender baseresin such as Nylobag™ Extender Base NB-381 (Sericol Group Ltd.,Westwood Road, Broadstairs, Kent CT10 2PA, England) with 1-5% ofNylobag™ or Nylotex™ hardener such as NB-386 (Sericol). Depending uponthe demands of the image or the climate, the reflective layer formulamay be modified to suit with Nylobag™ or Nylotex™ thinner (SericolGroup) and Nylobag™ or Nylotex™ retarder (Sericol). The reflective layermay be allowed to dry by standing at ambient temperature overnight.

The portion of the image which it is desired to transfer to fabric isprinted with a bonding layer, such as Sericol Nylobag™ or Nylotex™extender base (Sericol Group Ltd.) through a 137-150 mesh T threadscreen. Immediately after printing and while the image is still wet, adry transfer adhesive powder such as Tubitrans Elastomelt 95F (CHT NorthAmerica, P.O. Box 467, Lynchburg, Ohio, 45142) is applied to theretroreflective transfer sheet material such that the entire image isuniformly covered with powder transfer adhesive. Excess powderedtransfer adhesive is removed from the image areas by gentle shaking, andthen the transfer print is allowed to dry at ambient temperature for atleast two hours, preferably overnight. After drying, any additionalexcess powdered transfer adhesive which is not shaken from the imagewhile still wet may be removed by firmly brushing the dry image with asoft brush. The powder transfer adhesive on the surface of the transferprint may be further set by melting. This may be accomplished by passagethrough a screen printing drying unit equipped with radiant heating atsuch a speed that only the surface of the image becomes smooth andglossy while no damage is done to the transfer sheet material. One waythis may be accomplished is with a Texair Model 30 screen printing oven(American Advance Screen Printing Equipment Company, 400 North NobelStreet, Chicago, Ill., 60622-6383) set at 100° F. (38° C.) forced air,900° F. (482° C.) radiant, and belt speed No. 1.

The resulting transfer may be transferred to a number of fabricsubstrates by heat lamination. A Hix Model N-800 heat lamination machine(Hix Corporation, 1201 E. 27th, Pittsburg, Kans., 66762) set at 160° C.,45 pounds (20 kg) feed air pressure, and close time of 12-15 seconds ispreferred. After the laminated construction is cooled to roomtemperature, the liner may be removed to reveal the retroreflectivetransfer image laminated to the fabric substrate.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention. For example, while the invention isparticularly adapted to retroreflectorization of fabrics and otherflexible substrates, and is discussed herein particularly in thatcontext, the invention is also envisioned to be useful inretroreflectorizing other substrates. Further, it is also contemplatedthat sheet materials of the invention could be used to producefree-standing characters by transferring the design of the sheetmaterial to a temporary substrate, and then removing the design from thetemporary substrate by, for example, reheating the substrate to weakenthe adhesive strength of the bonding layer.

What is claimed is:
 1. A transfer sheet material for forming retroreflective graphic images on a substrate, the sheet material comprising:a) a monolayer of transparent microspheres; b) a color layer printed over the microspheres in a first graphic segment of the sheet material in an imagewise pattern, the color layer comprising a colorant in a transparent resin; c) a reflective layer printed over the microspheres in a second graphic segment of the sheet material in an imagewise pattern in such a manner that any overlapping areas of the first and second graphic segments are characterized by the color layer being disposed between the microspheres and the reflective layer, the reflective layer comprising reflective flakes in a transparent binder, wherein the microspheres are partially embedded in at least one of the color layer and the reflective layer, the reflective flakes being small enough relative to the microspheres that individual microspheres have the reflective flakes arranged in cup-like fashion about their embedded portions; and d) a bonding layer printed over the color layer and the reflective layer, the bonding layer being sufficiently thick to embed all exposed surfaces of the color layer and the reflective layer and being adapted for use in securing the sheet material to a substrate.
 2. The sheet material of claim 1 further comprising a second color layer printed in the first graphic segment in an imagewise pattern, the second color layer comprising a second colorant in a second transparent resin.
 3. The sheet material of claim 1 bonded to a substrate through the bonding layer.
 4. The sheet material of claim 3 wherein the substrate is a fabric.
 5. The sheet material of claim 1 wherein the reflective flakes are selected from the group consisting of metal flakes, plastic flakes, metal-plated plastic flakes, and nacreous pigment particles.
 6. The sheet material of claim 1 wherein the reflective flakes have a thickness in the range of about 0.03 to about 0.8 microns.
 7. The sheet material of claim 1 further comprising a carrier comprising a base sheet and a heat-softenable layer on the base sheet, the microspheres being embedded in the heat-softenable layer to a depth averaging between about 25 and about 50 percent of their diameters.
 8. The sheet material of claim 7 wherein the microspheres are embedded in the heat-softenable layer to a depth averaging between about 40 and about 50 percent of their diameters.
 9. The sheet material of claim 1 wherein the colorant comprises a transparent pigment.
 10. The sheet material of claim 1 wherein the colorant comprises a transparent dye.
 11. The sheet material of claim 1 wherein the transparent resin is selected from the group consisting of polyester resins and polyurethane resins.
 12. The sheet material of claim 1 wherein the transparent binder is selected from the group consisting of polyester binders and polyurethane binders.
 13. The sheet material of claim 1 wherein the color layer and the reflective layer at least partially overlap, the color layer being disposed between the microspheres and the reflective layer to provide a segment of the sheet material which is capable of retroreflecting the color of the color layer when the microspheres in this segment are illuminated with a beam of incident light.
 14. The sheet material of claim 1 wherein the bonding layer comprises an extender resin and a heat-activatable, hot-melt adhesive powder fused into the extender resin.
 15. The sheet material of claim 14 wherein the extender resin is selected from the group consisting of polyester extender resins and polyurethane extender resins.
 16. The sheet material of claim 14 wherein the hot-melt adhesive powder comprises a polymeric material selected from the group consisting of polyesters and polyamides.
 17. A transfer sheet material for forming retroreflective graphic images on a substrate, the sheet material comprising:a) a monolayer of transparent microspheres; b) a first colored reflective layer printed over the microspheres in a first graphic segment of the sheet material in an imagewise pattern, the first colored reflective layer comprising a colorant and reflective flakes in a transparent resin, wherein the microspheres are partially embedded in the first colored reflective layer, the reflective flakes being small enough relative to the microspheres such that individual microspheres have reflective flakes arranged in a cup-like fashion about the embedded portions of the microspheres; c) a second colored reflective layer printed over the microspheres in a second graphic segment of the sheet material in an imagewise pattern, the second colored reflective layer comprising a colorant and reflective flakes in a transparent resin, wherein the microspheres are partially embedded in the second colored reflective layer, the reflective flakes being small enough relative to the microspheres such that individual microspheres have reflective flakes arranged in a cup-like fashion about the embedded portions of the microspheres; and d) a bonding layer printed over the first and second colored reflective layers, the bonding layer being sufficiently thick to embed all exposed surfaces of the colored reflective layers and being adapted for use in securing the sheet material to a substrate.
 18. The sheet material of claim 17 wherein the reflective flakes comprise metal flakes.
 19. The sheet material of claim 17 wherein the reflective flakes comprise aluminum flakes.
 20. The sheet material of claim 17 further comprising:e) a layer of specularly reflective metal adhered to the microspheres in a third graphic segment of the sheet material in an imagewise pattern, the bonding layer being printed over the specularly reflective metal in the third graphic segment, the bonding layer being sufficiently thick to embed all exposed surfaces of the specularly reflective metal layer.
 21. The sheet material of claim 20 wherein the specularly reflective metal comprises aluminum.
 22. A transfer sheet material for forming retroreflective graphic images on a substrate, the sheet material comprising:a) a monolayer of transparent microspheres; b) a layer of specularly reflective metal adhered to the microspheres in a first graphic segment of the sheet material in an imagewise pattern; c) a color layer printed-over the microspheres in a second graphic segment of the sheet material in an imagewise pattern, the color layer comprising a colorant in a transparent resin; d) a reflective layer printed over the microspheres in a third graphic segment of the sheet material in an imagewise pattern in such a manner that any overlapping areas of the second and third graphic segments are characterized by the color layer being disposed between the microspheres and the reflective layer, the reflective layer comprising reflective flakes in a transparent binder, wherein the microspheres in the second and third graphic segments are partially embedded in at least one of the color layer and the reflective layer, the reflective flakes being small enough relative to the microspheres that individual microspheres have the reflective flakes arranged in a cup-like fashion about their embedded portions; and e) a bonding layer printed over the color layer, the reflective layer, and the specularly reflective metal layer, the bonding layer being sufficiently thick to embed all exposed surfaces of the color layer, the reflective layer, and the specularly reflective metal layer, and being adapted for use in securing the sheet material to a substrate.
 23. The transfer sheet material of claim 17, wherein the colorant comprises a pigment or dye. 